1. Field of the Invention
The present invention relates to a dispersion with excellent storage stability that employs a cellulose derivative as a plant-derived starting material, and specifically it relates to an aqueous coating composition with excellent curability obtained using the dispersion, that can form coating films with excellent coating workability, solvent resistance, chemical resistance and water resistance.
2. Description of the Related Art
Cellulose derivatives such as cellulose acetate butyrate are widely used as rheology controlling agents in the field of coating compositions.
Acrylic resins are also grafted onto cellulose derivatives, as disclosed in Japanese Unexamined Patent Publication SHO No. 56-163159, for use not only as rheology controlling agents but also for use of the cellulose derivatives as base resins, because of their excellent coating film performance including water resistance and solvent resistance, and their excellent sag resistance during coating and their superior coating appearance.
On the other hand, development of environmentally-friendly products continues to advance in the coating composition industry, as environmental pollution increases and society shifts toward greater recycling with the aim of reducing the burden on the environment. In light of these circumstances, and from the viewpoint of minimizing global warming and preventing deterioration of the indoor environment by reducing carbon dioxide gas emission, it has been a goal to develop coating compositions which, while naturally containing low amounts of volatile organic compounds (VOC) such as toluene and xylene, also employ plant-derived starting materials and biodegradable materials as carbon neutral starting materials from the viewpoint of reducing soil contamination after disposal.
Cellulose derivatives are useful starting materials in this sense, but their use in aqueous systems is problematic, particularly from the standpoint of storage stability. Emulsifiers are generally used for dispersing the cellulose derivatives in water, but the use of emulsifiers leads to problems such as reduced coating film performance, including durability and water resistance. Methods that do not use emulsifiers have also been developed.
Japanese Unexamined Patent Publication SHO No. 53-21225 discloses a water-dispersible cellulose graft polymer obtained by grafting an ethylenic unsaturated carboxylic acid-containing vinyl monomer onto the maleic anhydride reaction product of a cellulose ester derivative.
Japanese Unexamined Patent Publication SHO No. 60-123501 also discloses a carboxylated cellulose ester having an acid value of 5 or greater and an inherent viscosity of 0.01-1.00.
However, these resins have high viscosity in water and can only produce low solid content coating compositions, while their storage stability is also inadequate.